The invention relates to a process for the hydroformylation of olefins to produce aldehydes.
A number of hydroformylation processes involve the further processing of vent streams from hydroformylation reactors. The purpose of the vent streams is to prevent the accumulation of inert impurities, such as N2, CO2, Ar, CH4 and hydrocarbons, by purging them from the process. The inerts may get into the process as impurities in the feeds. These are generally vented prior to the product-catalyst separation zone to reduce the load on the separation systems. Unfortunately, venting these inerts also tends to lose valuable reactants, such as olefin.
There have been a number of disclosures teaching how to recover and recycle the olefin contained in these vents. Examples of these vent reactor processes are disclosed in GB 1,387,657 and U.S. Pat. Nos. 4,593,127, 5,105,018, 5,367,106, 5,675,041, 6,482,992, 6,969,777 and 7,405,329. Each process has a product-catalyst separation zone for each reactor system. In several cases, the product-catalyst separation step is performed in the hydroformylation reactor vessel in a so-called “gas-recycle” system as described in U.S. Pat. No. 4,247,486.
U.S. Pat. No. 5,367,106 teaches sending the reactor vent stream sent to a second, plug flow reactor. There are effectively two product-catalyst separation zones in this complex scheme, the first being in the primary reactor and the second being a pair of flashpots off of the plug flow reactor.
CN 102826973 teaches sending the liquid output of the first reactor to a syngas stripper to remove the olefin prior to the product-catalyst separation zone. The effluent streams of all the reactors feed into the syngas stripper prior to entering the product-catalyst separation zone. The process discards the final reactor vent as well as the vent from the vaporizer, which may contain substantial amounts of unreacted olefin. It is known from U.S. Pat. Nos. 4,277,627 and 5,675,041 that exposure of catalyst solution to high levels of syngas can degrade catalyst life. It is not economical to send catalyst-containing streams containing some of the most common hydroformylation ligands, such as triphenylphosphine, to the syngas stripper, since at the bottom of the stripping column the catalyst will be exposed to elevated CO partial pressure and elevated temperature in the absence of olefin, thereby causing catalyst deactivation.
CN 103130623 discloses a process that uses a compressor to pressurize the vent stream from the first reactor into a second reactor. The combined output of both reactors is sent to a syngas stripper before product-catalyst separation.
CN 101293818 shows a flowsheet wherein the each reactor has a distillation unit wherein unreacted olefin is removed. In order to efficiently remove the olefin from the first reactor effluent, this distillation involves a substantial capital investment. The combined output of the reactors is then sent to a product-catalyst separation zone. The use of multiple vaporizers means repeated exposure of the catalyst to harsh conditions which promote ligand and/or catalyst degradation and heavies formation.
The above schemes involve complex, expensive designs. It would be desirable to have a hydroformylation process capable of maintaining high olefin conversion, but at lower capital cost. It would also be desirable to have an improved process that is more compact, with lower catalyst requirements.